Content Purchase Request

I need your advice. I am new in video production industry. Self learner, passionate freelance photo/videographer with just a few ambitious project so far.
I got this email from film producing company. Currently they work on the airline advertisement and ask to purchase content of my video.
They need some portions of the video, approximately 6sec long all together.
It will be exposed through world-wide corporate web&youtube up to 6months.
On the top of that they intend to pay the permission of usage.